Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$27.78	7.660%	$29.9079	$29.91	$29.90	$29.90
Purchase #2	$72.91	7.539%	$78.4067	$78.41	$78.40	$78.40
Purchase #3	$138.70	6.231%	$147.3424	$147.34	$147.35	$147.30
Purchase #4	$9.73	13.242%	$11.0184	$11.02	$11.00	$11.00
Purchase #5	$241.66	12.319%	$271.4301	$271.43	$271.45	$271.40
Purchase #6	$5.82	8.870%	$6.3362	$6.34	$6.35	$6.30
Purchase #7	$197.92	12.109%	$221.8861	$221.89	$221.90	$221.90
7 purchase totals =	$694.52		$766.3278	$766.34	$766.35	$766.20